People, especially elderly people, may suffer from osteoporosis. One aspect of osteoporosis may be the partial or complete collapse of the bony structure of the spine, which in turn can cause loss of vertebral height, fracture of a vertebral disc, facet and nerve impingement, etc. Collapse of the spine often results in, for example, pain, reduction of lung function, unbalanced stature, etc. One treatment option may be a surgical procedure to re-align the vertebra (e.g., to re-establish balanced curvature of the spine as well as the intervertebral disc space).
Re-alignment of a spine including a damaged vertebra or disc may be accomplished by replacing the damaged vertebra, disc or portions thereof with an intervertebral implant. That is, an intervertebral implant may be inserted into the intervertebral disc space of two neighboring vertebral bodies or into the space created by removal of portions of or the entire vertebral body after removal of damaged portions of the spine. Preferably, the intervertebral implant restores the spine, as much as possible, to a natural state, i.e. to restore the original height of the intervertebral disc or the series of vertebra and, thus, the original distance between the two neighboring or adjacent vertebral bodies or vertebral bodies in various levels of the spine.
Typically implantation of one or more intervertebral implants is not part of a treatment procedure for osteoporosis. One reason for this may be that intervertebral implants are often designed with high structural stiffness. Osteoporotic bone is usually brittle, thus increasing the risk of breaking a vertebral endplate during a surgery or implantation of an implant and the endplates may have a uneven surface. For example, a stiff implant may impact a point or small area of an uneven surface of the osteoporotic bone, thereby creating a stress concentration and potentially damaging the bone. Therefore, the incorporation of an intervertebral implant in certain cases, is contra-indicated for patients with osteoporotic bone. Another reason for not incorporating an intervertebral implant may be that the insertion approach for implanting an intervertebral implant is difficult and risky, especially in elderly patients.
Alternatively, rather than implanting an intervertebral implant, a surgeon may elect to perform a Vertebralplasty and/or Cavitoplasty procedure on the patient's spine. In an exemplary method of performing a Vertebralplasty and/or Cavitoplasty procedure, a protective sleeve or cannula may be inserted into the patient's body, adjacent to the patient's spine. The spine may then be re-aligned if fractured or re-fractured. Next cement is inserted into the spine to replace lost bone and/or to limit future cracks. After the hardening of the cement, the treated section of the spine may be re-aligned and the patient may then return to his or her daily activity. In a Cavitoplasty procedure, a cavity may be formed in one or more of the vertebral bodies for receiving a portion of the cement.
It would be desirable to construct an intervertebral implant that is relatively simple to insert into a patient's spine at a relatively small size and which is able to expand to restore the original height of the removed spinal material or to a height desired by a surgeon. It would also be desirable to construct an intervertebral implant that is adaptable to uneven surfaces of an osteoporotic vertebral bone to limit stress concentrations when the implant is expanded and contacts or applies pressure to a patient's endplate.